The overall objective of this project is to determine the role of surface-associated antigenic colonization factors of enterotoxigenic E. coli (ETEC) in human diarrhea. Goals accomplished during the current year were: improved purification of the E. coli H-10407-type colonization factor antigen (CFA/I) and characterization of CFA/I in terms of (1) molecular composition and (2) hemagglutination and adhesive properties; demonstration of the role of CFA/I of E. coli H-10407 as a virulence factor for man employing groups of volunteers challenged with living E. coli with and without the antigen, and demonstration of anti-CFA/I humoral antibody responses in serological studies performed with orally challenged volunteers (above) and with sera from ETEC cases and appropriate controls in the field. Goals set for the coming year are (1) to investigate the immunology of ETEC colonization factor antigens by studying both active and passive immunity in experimental animals; (2) to continue development of new and efficient tools for the detection of bacteria possessing CF antigens and (3) to use the newly developed technology to elucidate the immunology of CF antigens of ETEC in man and provide a background for vaccine development.